In electrospray, very small droplets can be produced, but it is difficult to set up and only works with conductive surfaces and requires use of a high voltage (>3000V). The coating process is very long because flow rates are typically <5 μL/min (30 min to 1 hr/sample). Components of the electrospray system are prone to clogging because of high concentrations of matrix employed. Also, only one sample at a time can be processed, which slows down the process. In addition, electrospray systems can only produce a very thin coating, which may be insufficient to desorb ions without causing significant ion fragmentation or not provide a high intense signal for low abundant species.
Another technique is inkjet printing, but inkjet printing is incompatible with strong solvents such as chloroform and low pH solutions. In addition, the process for coating is long (e.g., over 30 min/sample). Also, inkjet printing is prone to clogging and the lifetime of the printer is very short (<6 months).
Airbrushing is another technique that can be used to form a layer of matrix. Airbrushing is problematic because uniformity and reproducibility of the matrix layer is often difficult to control. In addition, the process for coating is long (e.g., over 30 min/sample) and only one sample at a time can be processed.
Dry coating is yet another technique, and it works by shaking matrix powder onto a sample, but reproducibility is problematic and matrix incorporation into the tissue is minimal.
Thus, there is a need to provide an alternative approach to the one noted above.